Lee Anne Willson, Physics and Astronomy, (515) 294-6765
George Bowen, Physics and Astronomy, (515) 294-7659
Skip Derra, News Service, (515) 294-4917


AMES, Iowa -- It may take some time, but Earth will see a fiery end to its existence, say two Iowa State University astronomers.

Lee Anne Willson, an Iowa State University professor of physics and astronomy and George Bowen, professor emeritus of physics and astronomy, say new computer models of the later stages of the Sun's life show that it will expand and engulf our planet before it shrinks back in size and fades away as a white dwarf.

"Earth will get scorched as part of the process the Sun will go through as it transforms from being a red giant into a white dwarf," said Willson, who will present the research at the annual meeting of the American Association for the Advancement of Science, Feb. 17-22, in Washington, D.C.

Most astronomers agree that as the Sun evolves over the next 5 thousand million years, it will become about twice as bright as it is today. However, when the center of the Sun runs out of fuel and the Sun becomes a red giant, it will grow much brighter and larger. At question is the maximum size the Sun will reach and whether Earth will be able to get out of the way before the Sun gets too big.

Willson and Bowen studied the mass loss of red giant stars and used that information to predict the fate of the Sun and its effects on the planets. Their computer models are able to predict in great detail the conditions that Earth and the other planets will encounter as the Sun ages. Willson and Bowen's research predicts a fiery end to our planet.

"We know stars like the Sun lose about 40 percent of their mass during their advanced red giant evolution," Willson said. "However, it has not been clear whether that mass comes off very gradually, over millions of years, or relatively abruptly, over the last tens or hundreds of thousands of years. And that turns out to make all the difference in the world."

From detailed computer models of the rate of mass loss of red giants, also known as Mira variables, Bowen and Willson have found that the final mass loss process ramps up steeply only near the very end of the red giant stage, and therefore is over in a much shorter period of time, not giving Earth much of a chance to get out of the way.

"The Sun will expand and include Earth's orbit (a distance nominally of 93 million miles) before the Sun loses enough mass to let Earth move away," Willson said. "Most likely, the Sun will expand to hide the Earth for a few centuries and then retreat to reveal it, still mostly intact, at least once before the end."

Like in real estate, the planets will find that location is everything.

"We are confident that Jupiter, Saturn, Uranus and Neptune (the large, gaseous outer planets) will survive after the Sun fades to a dim remnant," she adds. "We are not sure about Mars. Mercury and Venus? They're toast long before Earth gets into trouble."

Willson's presentation is part of a session she organized for the AAAS meeting. The session, "The Far Future Sun and the Ultimate Fate of the Earth," will be held 9 a.m.-12 p.m., Feb. 20.

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